I have no relevant experience, but here's a "diccionario chicano-español" which says that "traila" (which doesn't really need an accent but often seems to get one) is the same thing as "tráiler" or "camión":
"Traila (tráila): Tráiler, camión"
http://www.mty.itesm.mx/dhcs/deptos/co/co95-832/proy_2006_S1...
In any case, "tráiler" as a synonym for "remolque" is not confined to US-Mexican Spanish or even Mexican Spanish in general; it is listed in the DRAE. So that would suggest that "traila" is a US Spanish variant of "tráiler" (approximating more closely to EN pronunciation). As for "tráiler" vs. "camión", of course they're not synonyms, but I think the point is that "tráiler" can be applied to the truck with semi-trailer or trailer: a big rig, as you call it. As Neil says, I doubt the distinctions are too precise here.
The translation workplace 
